An electronic structure description of atom and electron transfer in sulfite oxidase

Journal

of Inorganic

biochemistry

ructure Description of Atom an

96 (2003)

lect

ans

Martin L Kirk, The University ofNew Mexico, United States Katrina Peariso, 78e University ofNew Mexico, United States The sulfite oxidase (So) family of mononuclear molybdenum enzymes fu~~~io~sto catalyze various ~~~~~~~~~tro~ redo% reactions coupled to formal oxygen atom transfer. In vertebrates SO is found in the rn~to~bon~r~a~i~ter~~~mbr~e space, where the physiologically important oxidation of sulfite represents the terminal step in the oxidative degr~~~t~~nof cysteine and methioni~e. Individuals who suffer from isolated sulfite oxidase deficiency, which derives from s~~~~~~ mutations in the So gene, display a variety of deleterious effects including neurological abnormalities, disl~6ati01~ of the CC&X lens, rne~~a~ ation, and even attenuated brain growth. We have used small molecule analogues of oxidized (SOJ and reduced (SOJ SO in order to provai-e deeper insight into their mechanism of activity. Deconvoluting the different contributions of thiolate and ene-i ~2~dit~~~o~ate the ~~der~yi~gelectronic structure of the MO site in SO has proven to be a di~cu~t task. We have used de ~a~c~Iat~o~s in order to probe the effects of these S donor ligands on SOa?.in the oxygen atom transfer oxidative half-reaction, these differences in S donor ability may be illuminated bj selectively subs~t~t~~~Se complexes which possessmultiple sulfur donor ligand environments. As such, we will discussthe sy~tb~sis~structures, and detailed spectroscopyof new oxo-MO(V) complexes as effective models for the one electron reduced active site of $0. These studies have provided much needed insight into the electronic structure of the reduces SO site, an a]~Qwc~for ~~~reas~d understanding of the individual roles played by these different thiolate donors in electron transfer re~~~era~io The results of this work are also being used to ascertain the electronic origin of the enzyme e~$~t~o~~~ ESEEM, and ENDOR spectra, and to develop deeper insight into the e~e~tro~~~ structure ofthe SO site.

nctio

H-S

Norikazu Ueyama Department Koji Baba, Japan Taka-aki Okamura; Department

Hydrogen Bond in of Macromolecular

Science, Graduate

School ofScience,

of Macromolecular

Science, Graduate

School ofScience,

k)saka Lhr’versi~~~ ~a~~~~~

‘~~~gste~~-oxidases have been considered to catalyze oxo-transfer reaction wit kinetic advantages at high se model complex, v”O2(bdt)$ (bdt = benzenedithiolate), exhibits relatively high oxo-transfix r~a~t~~~t~, with the corresp ing [Mov’0,(bdt)J2-, in a mode1 C-H oxidation reaction using benzoin. The o mes &om a m trans influence of thiolate sulfur at the trans osition ofW=O. The presence o tween pterin amine NH and dithiolene sulfur is proposed in bo oxidized and reducecjstateshas data reported for various MO- and W-oxidases. The crystal structure of a novel model compl (~eC~~H~~~~~~~~~,indicates the existence of strong NH-S hydr bond between ami (2.46 angstroms for NH-S distance) at trans position of W=Q but n S hydrogen bond position of W=O, as supported by IR data for amide M% in the solid state and in CEI$~ soluti position of W=O have a strong covalent character like Hg-S bond in a linear ~g(IX) thiolate at the trans position of W=O have a relatively ionic one. The NH-S hydrogen bond does no at the trans position of W=O while definitely decreasesoxo-transfer reactivity in a model oxi In addition, the observation of only a weak W=O Raman signal suggeststhe decrease of LMGT from . Thus, NH-S hydrogen bond toward dithiolene sulfur at the trans positio stare to decrease oxo-transfer reactivity.